Method for controlling gear definition in an automated stepped gearbox

ABSTRACT

A method for controlling the gear release in an automated multi-speed drive in a vehicle drive with a drive motor and a separating clutch positioned between the drive motor and the multi-speed drive that the events “application of a shifting power” and “opening of the separating clutch” are determined dependent on reaching certain vehicle accelerations (a gear     —     release , a clutch     —     engage ). The vehicle acceleration (a veh ) decreases at the beginning of the shifting process due to the reduction of the fuel injection quantity (EM) supplied to the drive motor.

This application is a national stage completion of PCT/EP02/07200 filedJun. 29. 2002 which claims priority from German Application SerialNo.101 32 738.2 dated Jul. 5, 2001.

FIELD OF THE INVENTION

The invention concerns a method for controlling the gear release in anautomated multi-speed drive for motor vehicles.

BACKGROUND OF THE INVENTION

A system-dependent tractive force interruption takes place when shiftinggears in automatic multi-speed drives. Normally the following processestake place when shifting a gear:

-   -   reduction of the torque transferred from the drive motor    -   engaging of the separating clutch    -   release of the old gear    -   engagement of the new gear    -   disengaging of the separating clutch    -   increase of the transferred torque by an amount that corresponds        to the appropriate pedal position.

Shifting should take place quickly especially in the case of hightractive power requirements, such as in inclinations in order to avoid aslow-down of the vehicle during shifting. In addition, comfort criteriamust be maintained and the load of the shift elements must remain withincertain limits. Depending on the driving situation, a different timesequence is necessary for the process steps, so that the shift period,comfort, and load criteria can be maintained.

DE 198 02 736 A1 discloses a method where the speed of the torquedecrease at the start of the shifting process and of the torque increaseat the end of the shifting process is determined depending on thevehicle acceleration and the gas pedal angle. According to this knownmethod, the clutch is engaged and the gear is released at the end of theramp with which the torque is reduced. In certain driving situations,the timing for engaging the clutch is too early or too late comparedwith an optimal shifting operation.

The present invention is based on the task of developing a method forcontrolling the gear release where the time sequence of the processsteps while releasing the gear can be optimized in a simple fashion.

This problem is solved according to the inventive method. Accordingly,the steps—application of a shift load for decoupling the shift elementsand opening the separating clutch—are triggered at that point when thevehicle acceleration, which is continuously determined at each programstep, reaches an assigned vehicle acceleration value. During the startof the shifting process the current initial acceleration of the vehicleis determined and stored in the memory of the electronic control system.Then the torque of the drive motor is continuously reduced by loweringthe injected fuel quantity supplied by the fuel injection pump. At thebeginning of the shift, a first and second vehicle acceleration value isdetermined dependent on the starting acceleration of the vehicle, theinjected fuel quantity that is supplied to the drive motor and theengaged gear. The current vehicle acceleration is constantly comparedwith the first and the second vehicle acceleration values. As soon asthe current vehicle acceleration reaches or falls below the firstvehicle acceleration value, the actuator is applied with a shift powerfor the shift elements to be decoupled, so that consequently the gear isreleased.

SUMMARY OF THE INVENTION

The current vehicle acceleration is also constantly compared with thesecond vehicle acceleration value. As soon as it reaches or falls belowthe second vehicle acceleration value, the clutch actuator will engagethe clutch. This can take place after the application of the shift powerto the shift elements that are to be decoupled, especially with highstarting acceleration values. As the first and the second vehicleacceleration values are determined independently from each other, it isalso conceivable that the value reaches or falls below the secondvehicle acceleration value first. In this case, however, the shift poweris applied also to the actuator for the shift elements that are to bedecoupled at the latest now because the transferred torque in the driveis so small that the shift power applied by the actuator is sufficientfor decoupling the shift power elements.

The determined vehicle acceleration which, for example, can be measuredor calculated by deducing a speed value, is a very good indicator forthe actual torque that is transferred by the drive at any moment. As thestate of the vehicle is extremely transient during shifting othermethods that depend on the motor load often deliver results that areoffset in time. The first and second vehicle acceleration values aredependent on the fuel injection quantity supplied to the drive motor andon the engaged gear or on the gear range in maps that had been stored inthe memory of the electronic control system, which is accessed with eachprogram run.

In an advantageous design of the invention, the torque transferred fromthe drive motor is reduced with a speed that depends on the startingacceleration of the vehicle and on the applied gas pedal position at thestart of the shifting process.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with referenceto the accompanying drawings in which:

FIG. 1 shows a flow chart of the method according to the invention; and

FIG. 2 shows the time sequence of the gear release.

DETAILED DESCRIPTION OF THE INVENTION

A method step 2 presents the start of the shift at the time t₀, showinga status just before the shifting process. At method step 4 at the timet₀, the current initial vehicle acceleration a_(start) is determined atthe start of the shifting process. It is the same as the current vehicleacceleration a_(veh) (t₀). In method steps 6 and 8, the two vehicleacceleration values a_(clutch) _(—) _(engage) and a_(clutch) _(—)_(release) are determined. The values for these vehicle accelerationsdepend on the initial vehicle acceleration a_(start), the fuel injectionquantity EM that is supplied to the drive motor and the engaged actualgear in the maps of the electronic control system. The two vehicleacceleration values a_(clutch) _(—) _(engage) and a_(clutch) _(—)_(release) are stored in the electronic control system and aresubsequently constantly—that is at every program run—compared with thecurrent vehicle acceleration a_(veh). The current vehicle accelerationthen decreases continuously due to the reduction of torque by the drivemotor. The speed dM/dt with which the torque that is supplied by thedrive motor is reduced is a function of the initial vehicle accelerationa_(start), and the gas pedal position FP (see program step 10). Duringthe following program step 12, the current vehicle acceleration a_(veh)is compared with the vehicle acceleration value a_(gear) _(—)_(release). If the current vehicle acceleration a_(veh) is smaller thanor equal to the vehicle acceleration value a_(gear) _(—) _(release) acommand is triggered in program step 14 causing the shift elements thatare to be decoupled to be supplied with the shift power by the actuator.As soon as the torque on the shift elements is small enough, the shiftelements to be decoupled are released due to the applied shift power andthe gear is released. The program step 16 will run a cycle until thecurrent vehicle acceleration value a_(veh) drops also below the secondvehicle acceleration value a_(clutch) _(—) _(release) until theseparating clutch is engaged in program step 18, ending the gear releasein program step 20.

As long as none of the two vehicle acceleration values a_(gear) _(—)_(release) and a_(clutch) _(—) _(engage) is reached or falls below it,the scanning is repeated in a loop in program steps 12 and 22. If thecurrent vehicle acceleration value a_(veh) drops below the vehicleacceleration value a_(clutch) _(—) _(engage) the separating clutch isopened on program step 24 and immediately thereafter the actuator isapplied with a shift power for the shift elements to be decoupled, whichends the function.

FIG. 2 shows the time sequence of the method steps according to theinvention. The chronological course of the fuel injected quantity EM isshown in the upper part of the diagram. The reduction of the fuelinjected quantity starts after the shift command at the time t₀ causingthe torque reduction of the drive motor. The increase at which the fuelinjected quantity is reduced during the time period t₀ to t₁ is ameasure for the speed dM/dt of the torque reduction by the drive motor.This speed depends on the initial vehicle acceleration a_(start) and thegas pedal position FP at the time of t₀. The speed of the reduction intorque by the drive motor is greater the greater the initial vehicleacceleration and the greater the initial gas pedal position is.

The course of the vehicle acceleration a_(veh) is shown in the secondpartial diagram. The current vehicle acceleration at the time t₀ is theinitial vehicle acceleration a_(start), which is used for determiningthe vehicle acceleration values a_(gear) _(—) _(release) and a_(clutch)_(—) _(engage). The current vehicle acceleration a_(veh) is reduced as aconsequence to the reduction in the fuel injected quantity at a timedelay. The time delay results partially from the time-delayed reactionof the drive motor. In addition, there are several components in thedrive train, especially the long universal joint shafts that deformelastically under load. The stored energy herein also decreases onlyslowly with the torque reduction by the drive motor.

The current vehicle acceleration a_(veh) reaches the vehicleacceleration value a_(gear) _(—) _(release) at the time t₂. It can beseen in the bottom partial diagram of FIG. 2 that the shift elements tobe decoupled are applied with a shift power at this time.

The current vehicle acceleration a_(veh) reaches the vehicleacceleration value a_(clutch) _(—) _(engage) at the time t₃. It can beseen in the third partial diagram of FIG. 2 that the clutch plate startsto engage the clutch at that time. The clutch is finally engaged at thetime t₄. At the latest at that point in time, the shift elements do nottransfer any torque to the shift elements to be decoupled causing themto be decoupled with a low shift power. The decoupling of the shiftelements can, however, take place already before engaging the clutch ifthe torque has an appropriate small value due to the reduction of thefuel injected quantity.

According to the invention, the events “application of the shiftelements to be decoupled with a shift power” and “opening of the clutch”do not always take place in the same given sequence. The vehicleacceleration values that trigger those events are determinedindependently from each other at the beginning of the shifting process.The coordination is significantly simplified as the values aredetermined at first independently from each other for different drivingsituations.

1. A method for controlling a gear release in an automated multi-speeddrive in a vehicle drive having a drive motor and a separating clutch,that is positioned between the drive motor and separating clutch andthat can be optionally opened or closed by a clutch plate whereby atorque of the drive motor is reduced at a start of a shifting process sothat shift elements to be decoupled during the gear release can bedecoupled by an actuator with little shift power and the torque of thedrive motor is not increased involuntarily by engaging the clutch,comprising the steps of: continuously determining a current vehicleacceleration (a_(veh)); determining a current initial vehicleacceleration (a_(start)) at the start of the shifting process;determining a first and second vehicle acceleration value (a_(gear) _(—)_(release), a_(clutch) _(—) _(engage)), dependent on the initial vehicleacceleration (a_(start)), a fuel injection quantity EM supplied to thedrive motor and the selected actual gear; constantly comparing thecurrent vehicle acceleration (a_(veh)) with the first and the secondvehicle acceleration values (a_(gear) _(—) _(release), a_(clutch) _(—)_(engage)); applying a shift force from the actuator on the shiftelements to be decoupled when the current vehicle acceleration (a_(veh))reaches the first acceleration value (a_(gear) _(—) _(release)) or dropsbelow it; and opening the clutch with the clutch plate when the currentvehicle acceleration value (a_(veh)) reaches or drops below the secondvehicle acceleration value (a_(clutch) _(—) _(engage)) whereby at thelatest the actuator applies a shift power to the shift elements to bedecoupled.
 2. The method according to claim 1, further comprising thestep of reducing the torque of the drive motor with a speed that dependson the initial vehicle acceleration (a_(start)) and a gas pedal position(FP) at the time (t₀).